Disclosed is a photoelectric conversion device, which can be manufactured by simple manufacturing steps, is capable of performing photoelectric conversion in a wide wavelength region, and has a high photoelectric conversion ratio also in the infrared wavelength region. A light detecting device and a light detecting method are also disclosed. The photoelectric conversion device (1) is provided with: a substrate (2) which contains a single crystalline titanium oxide; an adhering layer (2c) formed on the surface (2a) of the substrate (2); a metal fine structural bodies (3), which are disposed on the surface of the adhering layer (2c) at predetermined intervals in the predetermined direction, and each of which has a volume of 1,000-3,000,000 nm3; a container (4), which contains an electrolyte solution (L) in a region where the metal fine structural bodies (3) are disposed on the surface (2a) of the substrate (2); a conductive layer (7) formed on the rear surface (2b) of the substrate (2); and a counter electrode (5) in contact with the electrolyte solution (L) in the container (4). The metal fine structural bodies (3) are adhered on the substrate (2) with the adhering layer (2c) therebetween, and on the interface between the substrate (2) and the metal fine structural bodies (3), Schottky barriers are formed, and light in the infrared region is photoelectrically converted by means of plasmon resonance phenomenon.